1. Field of the Invention
The present invention relates to a protection circuit for a battery pack, a battery pack including the protection circuit and a method of operating the battery pack, and more particularly, the present invention relates to a protection circuit for a battery pack, and a battery pack including the battery pack and a method of operating the battery pack which includes controlling electric-charge/electric-discharge in not only a high temperature region but also a low temperature region, so that electrical-charge/discharge operation is controlled at high and low temperatures and the efficiency and safety are secured.
2. Description of the Related Art
As portable terminals, such as notebook PCs, mobile phones and so on, have been rapidly developed to be small and light, batteries used as driving power sources of these terminals increasingly need to be small and to have a high capacity. Specifically, since a lithium secondary battery has an operating voltage of 3.6V or more, which is higher three times that of a nickel-cadmium battery or a nickel-hydrogen battery, and has a high energy density per unit weight, it has been rapidly expanded in use.
However, when a lithium secondary battery is charged to be 4.5V or more, an electrolyte in the battery is dissolved, so that a gas is generated. Then, the inside pressure of the battery increases by the gas, to leak the electrolyte. Moreover, when the battery is discharged to be under a predetermined voltage, copper as a negative collector starts melting within the electrolyte, to deteriorate the performance of the battery.
Moreover, in light of a chemical characteristic of a battery, there is a high risk of firing, bursting or blasting upon over-charging, over-discharging or over-current by a short between terminals.
Therefore, a secondary battery includes a protection circuit module, together with a bare cell. The bare cell is formed by arranging an electrode assembly formed of a positive plate, a negative plate and a separator in a can formed of an iron or aluminum material, finishing the can using a cap assembly, injecting an electrolyte into the can, and sealing the can.
The protection circuit module prevents accidents from occurring by over-charging, over-discharging or over-current, to secure safety and reliability. After the bare cell is formed, the protection circuit module is positioned outside of the bare cell and is electrically connected to the bare cell.
The protection circuit module includes a protection circuit device and an electrode terminal on one side of a printed circuit board on which a wiring pattern is formed, and an external connection terminal to be connected to a terminal for employing a secondary battery on the other side thereof. The printed circuit board and the bare cell are connected to each other by a positive lead plate and a negative lead plate which respectively connect a positive and a negative terminal of the printed circuit board to a positive and a negative terminal of the bare cell.
After a space between the bare cell and the protection circuit module is filled by resin when the bare cell and the protection circuit module are connected to each other, a secondary battery is labeled or included in an external case, to form a battery pack. A battery pack is arranged in a portable terminal for use.
In a conventional pack, a charging or discharging operation occurs when the battery is connected to an external power source device or load through an external port. A path between the battery and the external port is a high current path used as a charge/discharge path, through which a relatively high current flows.
When a power source device is connected to the external port, a charging operation occurs. Then, a charge path is connected from the external port, charge element, temperature fuse and fuse to the battery.
When a load is connected to the external port, a discharging operation occurs. Then, a discharge path is connected from the battery, fuse, temperature fuse, discharge element and the external port to the load.
That is, the charge/discharge element alternately operates the charge element or discharge element according to a charge or discharge mode.
The battery outputs its internal information to primary and secondary protection circuits. The internal information includes the cell-related information, such as the temperature of a cell, the charge potential of the cell and the strength of an electrical current flowing in the cell. A sensor resistance senses the occurrence of over-charging or over-discharging and over-current and transmits sensing information to the primary and secondary protection circuits.
The primary protection circuit controls the charge/discharge element according to the cell-related information provided from the battery and the sensing information provided from the sensor resistance. The secondary protection circuit controls whether to blow the fuse according to the cell-related information provided from the battery and the sensing information provided from the sensor resistance.
When the temperature of the charge/discharge element is sensed and is above a rated temperature, both ends of the temperature fuse are off, so that the charge/discharge element is prevented from firing, burning or blasting due to an abnormal phenomenon.